#include <iostream>
#include <vector>
using namespace std;
int main() {
    int n;
    cin >> n;
    int ans = 0;
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < n; j++) {
            int temp;
            cin >> temp;
            if(i == 0 || i == n - 1 || j == 0 || j == n - 1) {
                ans += temp;
            }
        }
    }
    cout << ans << endl;

    return 0;
}